UNRAVELLING FUNCTIONAL INTERACTIONS OF THE RHODANESE-LIKE PROTEIN RhdA OF AZOTOBACTER VINELANDII

The subjects of the present investigation were A. vinelandii RhdA and E.coli SseA, that in the rhodanese-domain panorama represent two prototypes of tandem-domain rhodanese proteins. They belong to two different subfamilies: TSTs and MSTs and their active-site motifs, (CRXGX[R/T]) and (CG[S/T]GVT) respectively, are considered important in driving substrate recognition. In this work, multiple approaches were exploited with the aim of elucidating physiological role(s) of RhdA. We first focused on searching a possible metabolic pathway involving RhdA. Starting from the experimental evidence of direct sulfane sulfur transfer from E. coli IscS to RhdA (Forlani et al., 2005), we analyzed whether RhdA could function as sulfane sulfur acceptor of A. vinelandii cysteine desulfurases taking in account the importance of the trafficking of the persulfide in the biosynthetic pathways (Meuller 2006). Secondly, RhdA and SseA biological role(s) were investigated in vivo, taking advantage of the availability of an A. vinelandii mutant strain lacking rhdA gene (Colnaghi et al, 1996) and of an E. coli mutant strain lacking sseA gene (Celestini 2001). Different growth conditions in presence or in absence of oxidative agents have been evaluated, starting from the evidence that the RhdA null mutant MV474 was more prone than the wild-type strain UW136 to oxidative stress (Cereda et al., 2007).